"Most developed nations are wrestling with an aging population, longer life expectancies and falling birth rates," said Tracey Flaherty, senior vice president for government relations and retirement strategies at Natixis. But European nations are doing a better jobdealing with this tough combination thanks to strong government safety nets, such as Sweden's guaranteed pension program for all residents.

As people live longer, healthcare spending has also become a major issue for many retirees, said Flaherty.

The survey assessed health care conditions by looking at four factors: life expectancy, per capita health care spending, doctor and hospital availability and out-of-pocket spending.

Americans spent the most on health care per person,but lagged in access to care, sinking the U.S. to 23rd place for health care, the study found.Austria ranked highest in the category.

Quality of life, which measures factors like happiness and climate, was also a low point among American retirees -- namely due to environmental factors like pollution. Switzerland, a world leader in pollution control, came in first.

Per person, American retirees had one of the world's highest income levels. Yet, the vast income disparity among the population -- where thetop 10% control roughly 75% of the wealth -- pushed the U.S. to 38th place in terms of material well-being, the survey found.

And, when it came to finances, uncertainty about the ongoing viability of the Social Security program and Americans' ability to save enough for retirement pushed the country to 28th place.

The U.S.'s retirement security standing could fall even further in future years, as more and more workers rely on workplace 401(k) plans and individual savings instead of lifelong pensions, Flaherty said.

The Center for Retirement Research at Boston College recently predicted that 53% of workers 30 and older are unprepared for retirement.